Both Kenya and al-Shabab were reported to be sending reinforcements to the area along the Kenyan border district of Lagdera on Tuesday. Such skirmishes have not previously escalated into any wider violence.

Al-Shabab, an armed opposition group with links to al-Qaeda, controls much of southern Somalia bordering northeastern Kenya and is fighting to topple the UN-backed government in the Horn of Africa nation.

Local fears

The armed group staged its first attack outside Somalia on July 11, when it carried out twin suicide bombings in the Ugandan capital, Kampala, leaving at least 74 people dead.

However, there have been fears for some time in Kenya that the violence could spill over the long and porous border between the two countries.

Yusuf Ali Mohamed, a resident in the Somali town of Dhobley, told the Reuters news agency: "Here in Dhobley, al-Shabab are calling people to jihad against Kenya and deploying more fighters to the border.

"Local people fear new fighting between the two sides."

Kenya tightened security along its border with Somalia in February in anticipation of a government offensive against al-Shabab and other anti-government groups, which has yet to materialise. There were fears that Somali fighters might try and enter Kenya if attacked at home.

Kenya has twice been hit by al-Qaeda-linked attacks and while it cannot take part in the African Union peacekeeping in Somalia because it is a neighbour, the government has pledged to do what it can to prevent the chaos next door spreading.